There are concrete ships. Often these are barges, though traditional sail and powerboat designs are found (news to me as I wrote this comment, see Wikipedia link below).

I don't know how well the Roman formula would hold up, but traditional concrete tends to spall badly in constant exposure to salt water. Reinforced concrete suffers from rusting of the steel rebar segments.

Under dynamic stress, I doubt you'd get lifetimes of wear. Though several decades should be reasonably viable.

https://en.wikipedia.org/wiki/Concrete_ship